
// https://leetcode.cn/problems/number-of-islands/description/

class Solution
{
    int m, n;
    int dx[4] = { 0, 0, 1, -1 };
    int dy[4] = { 1, -1, 0, 0 };

public:
    int numIslands(vector<vector<char>>& grid)
    {
        int cnt = 0;
        m = grid.size();
        n = grid[0].size();
        for (int i = 0; i < m; ++i)
        {
            for (int j = 0; j < n; ++j)
            {
                if (grid[i][j] == '1')
                {
                    ++cnt;
                    dfs(grid, i, j);
                }
            }
        }

        return cnt;
    }

    void dfs(vector<vector<char>>& grid, int i, int j)
    {
        if (grid[i][j] == '0')
            return;

        grid[i][j] = '0';
        for (int k = 0; k < 4; ++k)
        {
            int x = i + dx[k];
            int y = j + dy[k];
            if (x >= 0 && x < m && y >= 0 && y < n)
                dfs(grid, x, y);
        }
    }
};